870 
Birge—The Crustacea of the Plankton. 
were found in the same species during the winter of 1895-6 and 
indeed similar tables could be constructed for any species fairly 
numerous, and neither increasing nor declining in numbers. 
On July 21 and August 15, 1896, a series of catches was made 
extending across the lake some 5 kilometers, at approximately 
equal distances. The result of the latter catch is given in the 
accompanying table; the other was substantially the same. 
Table XXVI.— Collections on August 18 , 1896 , expressed in thousands 
per square meter. 
I. 
II. 
III. 
IV. 
VI. 
VII. 
Diaptomus. 
27 
51 
40 
80 
74 
83 
Cyclops. 
184 
203 
142 
136 
127 
145 
D. pulicaria. 
57 
31 
3.3 
D. hyalina. 
37 
31 
15 
33 
33 
38 
D. retrocurva . 
13 
16 
7 
11 
3.3 
20 
Diaphanosoma. 
10 
18 
13 
27 
33 
49 
Chydorus. 
35 
217 
184 
154 
174 
147 
Leptodora . 
0.7 
1.5 
0.2 
0.5 
0.5 
Ergasilus. 
17 
16 
3.3 
8.9 
0.5 
Nauplii. 
241 
337 
1 
236 
134 
167 
Corethra. 
6 
8 
1.1 
1.2 
1.3 
4.4 
Asplancha . 
114 
101 
33 
66 
40 
45 
Total Crustacea. 
631.7 
921.5 
*407.6 
686.1 
678.8 
650 
* No nauplii included. 
The number of Cyclops when at its maximum showed sur¬ 
prisingly little variation. In 1895 from May 1st to June 6th, 
26 catches were made on 13 days. The catch ranged from 
10,000 to 20,000 individuals actually caught. In 1896, 18 catches 
were made on 16 days. The numbers ranged from 9,000 to 37,000. 
A figure is added (Fig. 21) showing the number of Cyclops 
caught during the year 1895. It will be seen that the diagram 
gives no warranty to the conclusion that this species appears 
in swarms. Similar illustrations could be taken from any year, 
and from almost any species, with the qualification that the range 
in number is greater in the case of those species whose num¬ 
bers are small. 
